AVS 45th International Symposium
    Surface Science Division Friday Sessions
       Session SS2-FrM

Paper SS2-FrM1
Dielectric Response and Ionization of Water Adlayers in High Electric Fields: Calculations and Experiments

Friday, November 6, 1998, 8:20 am, Room 309

Session: Water and Ice Interfaces
Presenter: E.M. Stuve, University of Washington
Authors: T.D. Pinkerton, University of Washington
D.L. Scovell, University of Washington
V. Medvedev, University of Washington
E.M. Stuve, University of Washington
Correspondent: Click to Email
Water/metal interfaces typically support high surface electric fields on the order of 1-3 V/Å (100-300 MV/cm) - fields strong enough to make or break chemical bonds. While the surface electric field depends upon electrode potential and the nature of both electrode and electrolyte, the response of the electric field to these parameters and its subsequent influence in electrochemical processes remain unknown. Controlled high surface electric fields can be obtained on sharp field emitter tips in vacuum through potentials of 1-5 kV applied to tips of radius 100-1000 Å. The response of both thin and thick water layers adsorbed on these tips thereby allows the influence of electric field to be probed directly. Theoretical and experimental results show the transition of the location of the field from the water/vacuum interface for thin water layers to the metal/water interface for water layers above 500 Å thickness. Ionization at the water/vacuum interface represents UHV adsorbed water, whereas ionization at the metal/water interface represents an electrochemical response. The field required for onset of ionization increases linearly with adlayer thickness, in agreement with calculations. With increasing field strength water ionizes to form H@sub 3@O@super +@, OH@super -@, and H@sub 2@O@super +@. These results demonstrate the electrochemical response of water as a function of field and have implications in basic electrochemistry, nanolithography, and the design of tips for field emitter arrays.